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Weak Immune System: Signs, Symptoms and Causes

Learn how to tell if your immune system needs help.

Amber Dowling, BJourn

Medically reviewed by

Ivor A. Emanuel, M.D.


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Feeling sick and tired all the time? Find out if your immune system needs help.

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Key takeaways
  • Your immune system is your body’s defense against invaders like viruses and bacteria.
  • Frequent infections, digestive distress, slow-healing wounds and fatigue can all be signs of a distressed immune system. 
  • Healthy habits like clocking a good night's sleep, eating well and exercising regularly can support your immune health. 

Your immune system is something special. It’s constantly working to expel pathogens  — disease-causing organisms such as viruses, bacteria, fungi and parasites — from your body. 

It takes detailed notes, too, developing antibodies to protect you from pathogens it’s seen before. You can think of your immune system cells like soldiers in your personal army, constantly looking out for potential enemies.

It’s a big job, so it’s no wonder that sometimes your immune system loses a battle or two in the overall war to keep you healthy. 

How does your immune system work?

Your immune system provides two major kinds of protection: innate immunity and acquired, or adaptive, immunity. 

Innate immunity

You were born with an innate immune system, the organs, cells and proteins that work to recognize foreign organisms when they enter through your skin or digestive system. Sometimes this part of your defense system is called the “non-specific immune system”¹ because it uses the same tools — leukocytes, or white blood cells — to fight different threats.

Acquired immunity, aka adaptive immunity

Acquired or adaptive immunity is something you develop over time. When you’re exposed to a particular pathogen, either through illness or through vaccination, your adaptive immune system fights and studies it at the same time, producing specific antibodies it can use later if it tries to hurt you again. Since this system is constantly adapting, it’s best equipped to handle viral infections that change over time.²

What are the signs of a weak immune system?  

Constantly getting sick is a strong indicator that you may have a problem with your immune system. Typical signs can include: 

  • Frequent colds, or a cold that lasts more than 10 days³
  • Frequent viral or bacterial infections
  • Digestive problems like frequent diarrhea or constipation
  • Slow-healing wounds
  • Feeling tired all the time

What causes a weak immune system?

There are hundreds of potential causes of immune system weakness, but these are some of the most common:

Immune system disorders

According to Johns Hopkins Medicine, there are four main types of immune system disorders:

  • Primary immunodeficiencies: You’re born with an immune system disorder, which you probably inherited.
  • Acquired immune deficiencies: You develop a disease that weakens your immune system. This could be a temporary deficiency caused by the flu, certain drugs or medications or poor lifestyle habits, or it could be a long-lasting or permanent deficiency such as AIDS. 
  • Overactive immune responses: Your immune army works too hard, treating harmless substances as threats. Allergic reactions to dust, plants and pet dander are examples of an overactive immune response.¹⁰ 
  • Autoimmune disorders: Your system starts fighting your own body. It’s unclear why some people are prone to autoimmune diseases such as celiac diseasediabetes and rheumatoid arthritis, but there is often a genetic link.¹¹

Lifestyle factors

Your habits and circumstances can affect your immune health. Some important lifestyle factors include: 

  • Stress: Do you tend to get sick after an especially hectic week at work? Research shows that long-term stress can weaken immune responses.¹²
  • Medications and other drugs: Certain medications, including chemotherapy drugs¹³ and steroids,¹⁴ can dampen immune health. So can drinking alcohol¹⁵ and smoking.¹⁶ 
  • Sleep: Getting regular and sufficient sleep is associated with better immunity, while sleep deprivation can suppress the system.¹⁷
  • Age: As we age, our immune defenses aren’t as quick to respond to new or previously encountered pathogens. This is a natural consequence of aging, so although you’re likely to get sick more often at 70 than at 20, it doesn’t necessarily signal an immunodeficiency.¹⁸ 

Can a doctor tell if you have a weak immune system?

Your healthcare provider can help diagnose immune problems. They may ask you about past illnesses or family history, or conduct a blood test to look at markers of immune health. There are also tests you can take at home to learn more about your immune system function.

How can you support your immune system?

If you’re feeling run down or just want to take extra precautions ahead of cold and flu season, there are several ways to support your body’s defenses. These include: 

  • Minimizing stress: We know stress can weaken immunity, so anything you can do to avoid stressors can help.
  • Getting enough sleep: For most adults, that means at least seven hours a night.¹⁹
  • Staying up-to-date on all of your vaccinations: Vaccinations can teach your adaptive immune system how to defend itself.²⁰
  • Practicing good hygiene: Washing your hands and avoiding touching your face can help prevent viruses such as colds and the flu.
  • Drinking alcohol in moderation and abstaining from smoking: Minimizing or avoiding alcohol intake can reduce its immune-dampening effects,²¹ while quitting smoking is always a good idea.
  • Exercising regularly: Regular exercise is associated with a range of health benefits, including stronger immune responses.²²
  • Eating lots of fruits and vegetables: The food you eat matters, and malnutrition has been shown to inhibit the production of antibodies and immune cells.²³


Every person has an innate and acquired immune system, which can be weakened by disease, age and other lifestyle factors. You can boost your immune system by getting good sleep, eating healthy food and avoiding smoking and drinking alcohol.

Updated on
February 22, 2024
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1.   National Center for Biotechnology Information, U.S. National Library of Medicine. How does the immune system work? Accessed February 10, 2022.

2.  PennMedicine. 6 Signs You Have a Weakened Immune System. Accessed February 10, 2022.

3.  Centers for Disease Control and Prevention. Common Colds: Protect Yourself and Others. Accessed February 10, 2022.

4.  American Academy of Allergy, Asthma & Immunology. Recurrent Infections May SIgnal Immunodeficiencies. Accessed February 10, 2022.

5.  National Center for Biotechnology Information, U.S. National Library of Medicine. The role of gut microbiota in immune homeostasis and autoimmunity. Accessed January 11, 2022. 

6.   Advances in Skin & Wound Care. Checklist for Factors Affecting Wound Healing. Accessed February 10, 2022. 

7.  Johns Hopkins Medicine. Disorders of the Immune System. Accessed February 10, 2022. 

8.  American Academy of Allergy, Asthma & Immunology. Primary Immunodeficiency Diseases (PIDD) Defined. Accessed February 10, 2022. 

9.  Johns Hopkins Medicine. Disorders of the Immune System. Accessed February 10, 2022. 

10.  Johns Hopkins Medicine. Disorders of the Immune System. Accessed February 10, 2022. 

11.   Johns Hopkins Medicine. Autoimmune Disease: Why Is My Immune System Attacking Itself? Accessed February 10, 2022

12.  American Psychological Association. Stress Weakens the Immune System. Accessed January 11, 2022. 

13.  American Cancer Society. Why People With Cancer Are More Likely to Get Infections. Accessed February 10, 2022.

14.  Centers for Disease Control and Prevention. Medications that Weaken Your Immune System and Fungal Infections. Accessed January 11, 2022.

15.  Alcohol Research. Alcohol and the Immune System. Accessed February 10, 2022.

16.  Centers for Disease Control and Prevention. Smoking and Overall Health. Accessed February 10, 2022.

17.  Communications Biology. Role of sleep deprivation in immune-related disease risk and outcomes. Accessed February 10, 2022.

18.  National Center for Biotechnology Information, U.S. National Library of Medicine. Causes, consequences, and reversal of immune system aging. Accessed January 11, 2022.

19.  Centers for Disease Control and Prevention. Sleep and Sleep Disorders. Accessed February 10, 2022.

20.  Centers for Disease Control and Prevention. The Immune System — The Body’s Defense Against Infection. Accessed February 2022.

21.  Alcohol Research. Alcohol and the Immune System. Accessed February 10, 2022.

22.  Clinical and Experimental Medicine.  Physical exercise as a tool to help the immune system against COVID-19: an integrative review of the current literature. Accessed February 2022.

23. Harvard T.H.Chan School of Public Health. Nutrition and Immunity. Accessed February 10, 2022.

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